I can only tell you that even in temperatures as low as -19C, coolant temperature was 83-84C on the highway once the engine was fully warmed up. On shorter trips and in -15C, coolant temperature was 81-82C but would dip down to 79 or 78C if load came off. Temperature drops pretty quickly at idle. I haven't had any experience in warmer ambient temperatures to know what coolant temperature runs in those conditions.

So I think I'm screwed up by this counterfeit t-stat. I need buy a new one again.
Do you guys go to dealers or is there a good aftermarket ones I can buy from some website?

Thanks

There are dealers that offer discounted prices online. You are better off using a BMW thermostat as BMW parts come with a 2-year warranty.

Actually any part not installed from an authorized dealer has no warranty. Any car manufacturer.

This is the first time I hear this and this official BMW page actually says it comes with 2 year unlimited mileage warranty with no fine prints or statement about only is installed by an authorized dealer: BMW Center Services - Overview - BMW North America

Now, from a practical level, they may pull the card of not being properly installed, but that's different than saying there's no warranty.

And btw, I'm sorry about this; I'm really not trying to pick on you...

No problem. From what I know any warranty on any part requires instalation in an authorized dealer. That is 100% true for any electric or electronic part. Once you take it out of the dealer uninstalled, it is yours forever. I didnt really think about a T-stat, but I cant imagine you will buy a water pump or transmission and you will go back after 23 months and get any kind of warranty, or even a discount on a replacement part.

On the topic of the transmission cooler thermostat, has anybody ever noticed or had a failure of that part?

I am as big a fan of unnecessary preventative maintenance as the next guy, but something like this seems like maybe you don't want to mess with it unless you have to. Especially because I can't see how a slightly cooler than normal transmission could have any ill-effects (based on nothing but my understanding of how cars work. Perhaps the ATF does require a small temperature range for optimal performance and minimal breakdown?)

Not correct. BMW's parts warranty is 2 years unlimited mileage providing the part was purchased from an authorized BMW dealer. It does not matter who does the installation thought I am sure anything obviously cocked up would be excluded. Labor for the warranty repair is covered if it is performed at a authorized BMW center. All is explained in SI B01 01 14.

Cheers.

Funny you should mention this... The bigger concern with the transmission cooler thermostat is (if I am reading the hose diagrams correctly) that if it fails open it will allow coolant to flow through the radiator and back into the engine - bypassing the main thermostat.

I recently had the main thermostat replaced (after arguing with the dealer for two weeks that it was bad - "can't be bad if there are no codes...") and immediately our temperatures went from 65-70C to 89-91C. This was in a Chicago winter and I was monitoring it one day with ambient at 4F and driving on the interstate it stayed steady at 89-91C (it would go a few degrees higher during DPF regen). We are now a few months later and the temperature has dropped to ~84C while cruising on the highway. In town it will creep up to around 90C. Theses are the classic signs to me that coolant is prematurely passing through the radiator. My next step is to replace the transmission cooler thermostat.

There have been many posts in this thread asking what the proper coolant temp is. Since these engines use an old school thermostat that is designed to begin to open at 88C the proper temps to look for are slightly above that - i.e. 89-91C. Anything less than that is an indication that "cooled coolant" is being sent to the engine before it is warranted and you have a failed or failing thermostat. Then the question becomes: "which one?"

Cheers.

BMW Service : Warranties

Original BMW Parts as well as Original BMW Accessories, a warranty of two years regardless of the mileage is offered. Service you can count on - we guarantee it.

Original BMW Parts : Remanufactured Parts

Yet every exchangeable part is subject to exactly the same quality specifications as a new BMW Part and it even carries the same 24-month warranty.

Neither mention the requirement that an authorized repair facility needs to do the installation. BMW does cover the labor of the installation of the part for 2 years if performed at a BMW dealer though.

So, if a dealer installs a part, the part and labor are covered for 2 years. If you or a non-dealer installs it, just the part is covered. If an indy did the install, they might warranty their own work though.

If you buy BMW floor mats and don't have the dealer install them, are you saying they wouldn't be covered?

If you bought a transmission and didn't have the dealer install but 1 year later first gear went out, you don't think BMW would honor the warranty if it was installed in a BMW? Wouldn't the Magnuson–Moss act come into play?